The relationship between mental health and drug and alcohol use is complex because one can effect the other.
Some drugs, such as cannabis, LSD, ecstasy, ice and speed, can directly produce effects that resemble symptoms of mental illness, such as hallucinations or paranoia. These effects usually disappear once the drug is out of the person's system.
However, many people who seek treatment for drug or alcohol problems also have mental health problems that are not due to their current drug use. These people tend to be more unwell and are more difficult to treat than people with a single disorder.
It has been suggested both that mental illness can cause drug problems (when a person takes drugs in the hope of escaping their symptoms), and that heavy drug use over time causes mental health problems. Most of the evidence, however, seems to indicate that the same factors can lead to both types of problems; that is, biological, social and/or environmental factors predispose a person to have both a mental health and a substance abuse problem.
Both drug and alcohol and mental health services have become much more aware of this situation, and best practice in both areas is now to treat both disorders if this is appropriate. If you are choosing a drug and alcohol treatment program for a friend or relative, it is important to ask whether they will help with any mental health problems.
If the client is a polydrug user, it is also important that the agency can treat each type of drug.